Multiple refrigerating device

ABSTRACT

A multi-type refrigerator is capable of achieving a high coefficient of performance (COP) while using R32 as refrigerant and that takes account of energy saving and global warming. Refrigerating cycles are executed by circulation of R32 as refrigerant through a refrigerant circuit including one outdoor unit having a compressor, a condenser, and expansion means and a plurality of indoor units having evaporators. A filling quantity of R32 for the refrigerant circuit is set in a range from 120 to 300 g/kW (refrigerating capacity). The filling quantity of R32 for the refrigerant circuit is set in a range from 84 to 300 g/L (internal volume of the condenser).

TECHNICAL FIELD

[0001] The present invention relates to a multi-type refrigerator havingan outdoor unit and indoor units in one-to-plurality correspondence, andmore particularly to a multi-type refrigerator in which R32 (having achemical formula CH₂F₂) or mixed refrigerant containing at least 70percent R32 by weight is used as alternative refrigerant to R22 (havinga chemical formula CHClF₂)

BACKGROUND ART

[0002] Among global environmental problems on refrigerators, airconditioners, and the like that execute refrigerating cycles with use ofrefrigerant are (1) ozonosphere protection, (2) energy saving, (3)countermeasures against global warming (reduction of emission of CO₂ andthe like), (4) reuse (recycling) of resources, and the like.

[0003] R22 (HFC22) that has conventionally been used has a high ODP(Ozone Depletion Potential) and is not suitable refrigerant, especially,in terms of ozonosphere protection among the global environmentalproblems. As alternative refrigerant to R22, there have been listedR410A (HFC32:HFC125=50:50 (by weight)), R407C(HFC32:HFC125:HFC134a=23:25:52 (by weight)) and the like. Amongrefrigerators that execute refrigerating cycles with use of R410A,R407C, or the like, refrigerators that have achieved COP (Coefficient ofPerformance) equivalent to COP obtained by R22 have already beencommercialized.

[0004] As for energy saving, there has been a notice that COP ofspecified air conditioners must be increased by approximately 4 percentnot later than the end of September in the year 2004 (Notice No. 190from the Ministry of International Trade and Industry of Japan, basedupon “the Law concerning the Rational Use of Energy”). Thus refrigeranthaving a large COP value is required to be used from viewpoint of energysaving.

[0005] Requirements for prevention of global warming have been gettingincreasingly stringent. Refrigerators, air conditioners, and the likeare evaluated with use of an index on global warming that is referred toas TEWI (Total Equivalent Warming Impact). TEWI is represented as thetotal of Global Warming Potential (GWP) and the inverse of COP.Accordingly, in order to prevent global warming, refrigerant having asmall GWP and a large COP has to be selected to decrease TEWI.

[0006] As refrigerant suitable for prevention of global warming may belisted R32 having a small global warming potential GWP. R32 has a GWPabout one-third that of R22, R407C or R410A, which is extremelyeffective for prevention of global warming.

[0007] As for COP of R32, COP value of R32 larger than that of R22 hasnot been obtained, while COP values of R407C and R410A are generallyequivalent to COP value of R22. That is to say, refrigerators thatexecute refrigerating cycles with use of R32 have not actually achievedCOP values that greatly exceed COP of R22, though such refrigerators aretheoretically expected to have high COP values in view ofcharacteristics of R32. Besides, there occur phenomena such as increasein pressure and discharge temperature relative to those with use of R22.In addition, slightly flammable R32 has a problem of difficulty inestablishing a consensus on safety thereof. Therefore, the industrialworld has never employed R32 as alternative refrigerant for actualproducts.

DISCLOSURE OF INVENTION

[0008] An object of the present invention is to provide a multi-typerefrigerator that is capable of achieving a high coefficient ofperformance (COP) while using R32 as refrigerant and that takes accountof energy saving and global warming.

[0009] The invention was created on basis of finding by the inventorthat trends of change in COP of refrigerators in response to quantity ofrefrigerant (total filling quantity for a refrigerant circuit) greatlydiffered among types of refrigerant, i.e., between R32 and otherrefrigerants such as R410A. Specifically, in use of R410A as shown inFIG. 1A, COP of R410A tends to increase gradually and to seem to becomesaturated with increase in the quantity of refrigerant in a range shownin the drawing. In use of R32, by contrast, COP of R32 tends to reachits peak with change in the quantity of refrigerant and tends todecrease while the quantity of refrigerant is out of a range thatprovides the peak. The reason why COP obtained with use of R32 has notexceeded COP obtained with use of R410A is that quantity of therefrigerant has been in a comparatively high range (from 1200 to 1300 gin an example of FIG. 1A). It should be noted that the peak value of COPwith change in quantity of refrigerant with use of R32 is much largerthan COP with use of R410A in an optimal quantity of refrigerant (1300 gin the example of FIG. 1A). It is thus found that a high COP may beobtained when the quantity of the refrigerant R32 is set in anappropriate range.

[0010] It has been found that R32 has GWP far lower and provides COPhigher than conventional R22 and R410A, and therefore, R32 has TEWIvalue lower than R22 or R410A to exhibit an excellent characteristic onglobal warming.

[0011] The multi-type refrigerator of the invention that executesrefrigerating cycles by circulating R32 as refrigerant through arefrigerant circuit including one outdoor unit having a compressor, acondenser, and expansion means and a plurality of indoor units havingevaporators is characterized in that a filling quantity ofabove-mentioned R32 for the refrigerant circuit is in a range from 120 gto 300 g per kilowatt of refrigerating capacity.

[0012] Thus high COP is obtained on condition that the filling quantityof R32 for the refrigerant circuit is in the range from 120 g to 300 gper kilowatt of refrigerating capacity.

[0013] The multi-type refrigerator of the invention that executesrefrigerating cycles by circulating R32 as refrigerant through therefrigerant circuit including one outdoor unit having the compressor,the condenser, and the expansion means and a plurality of indoor unitshaving the evaporators is characterized in that the filling quantity ofabove-mentioned R32 for the refrigerant circuit is in a range from 84 gto 300 g per liter of internal volume of the condenser.

[0014] Thus high COP is obtained on condition that the filling quantityof R32 for the refrigerant circuit is in the range from 84 g to 300 gper liter of internal volume of the condenser.

[0015] The multi-type refrigerator of the invention that executesrefrigerating cycles by circulating mixed refrigerant containing atleast 70 percent R32 by weight through the refrigerant circuit includingone outdoor unit having the compressor, the condenser, and the expansionmeans and a plurality of indoor units having the evaporators ischaracterized in that a filling quantity of above-mentioned R32 for therefrigerant circuit is in a range from 370 g to 700 g per kilowatt ofrefrigerating capacity.

[0016] With use of mixed refrigerant containing at least 70 percent R32by weight, high COP is obtained on condition that the filling quantityof R32 for the refrigerant circuit is in the range from 370 g to 700 gper kilowatt of refrigerating capacity.

[0017] The multi-type refrigerator of the invention that executesrefrigerating cycles by circulating mixed refrigerant containing atleast 70 percent R32 by weight through the refrigerant circuit includingone outdoor unit having the compressor, the condenser, and the expansionmeans and a plurality of indoor units having the evaporators ischaracterized in that the filling quantity of above-mentioned R32 forthe refrigerant circuit is in a range from 260 g to 700 g per liter ofinternal volume of the condenser.

[0018] With use of mixed refrigerant containing at least 70 percent R32by weight, high COP is obtained on condition that the filling quantityof R32 for the refrigerant circuit is in the range from 260 g to 700 gper liter of internal volume of the condenser.

BRIEF DESCRIPTION OF DRAWINGS

[0019]FIGS. 1A and 1B are diagrams showing results of measurement of COPwith use of R32 as refrigerant and COP with use of R410A, with variationin quantity of refrigerant (total quantity for filling a refrigerantcircuit), FIG. 1A showing the results in cooling operation, FIG. 1Bshowing the results in heating operation;

[0020]FIG. 2 is a diagram showing a schematic configuration of amulti-type heat pump air conditioner of an embodiment in accordance withan application of the invention;

[0021]FIGS. 3A and 3B are diagrams showing comparison between COP withuse of R32 and COP with use of R410A on condition that capacities arethe same (efficiencies of condensers are equivalent);

[0022]FIGS. 4A, 4B, and 4C are diagrams showing set values of aninternal volume of an indoor heat exchanger and an internal volume of anoutdoor heat exchanger of the air conditioner;

[0023]FIG. 5 is a diagram showing relationship between R32 contents inrefrigerant of R32 mixed with R125 and energy efficiencies;

[0024]FIG. 6 is a diagram showing relationship between COP and fillingquantities of refrigerant about R32 and R410A in cooling operation andheating operation; and

[0025]FIG. 7 is a diagram showing volumes of accumulators and receiversthat correspond to refrigerating capacities of refrigerants R32, R410A,and R22.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Hereinbelow, a refrigerator of the invention will be described indetail with reference to a preferred embodiment shown in the drawings.

[0027]FIG. 2 shows a schematic configuration of a multi-type heat pumpair conditioner of an embodiment in accordance with an application ofthe invention. In the air conditioner, a refrigerant circuit is composedof one outdoor unit 20 and a plurality of indoor units 1 that areconnected by refrigerant pipes 41 and 42, and R32 as refrigerant iscirculated through the refrigerant circuit. In each indoor unit 1 ishoused an indoor heat exchanger 2. In the outdoor unit 20 are housed acompressor 23 for compressing and discharging refrigerant (R32), afour-way directional control valve 25 for switching refrigerant passes,an outdoor heat exchanger 22, a motor-operated expansion valve 26, andan accumulator 24 for gas-liquid separation of returned refrigerant.

[0028] In cooling operation in which refrigerating cycles are executed,as shown by solid lines in FIG. 2, refrigerant discharged from thecompressor 23 is delivered through a pipe 31, the four-way directionalcontrol valve 25, and a pipe 33 to the outdoor heat exchanger 22functioning as a condenser, according to a switch setting of thefour-way directional control valve 25. The refrigerant condensed in theoutdoor heat exchanger 22 is delivered through a pipe 36, the expansionvalve 26 that throttles a pass to expand refrigerant, and the pipes 42to the indoor heat exchangers 2 functioning as evaporators. Therefrigerant vaporized in the indoor heat exchangers 2 is returned to thecompressor 23 through the pipes 41, a pipe 34, the four-way directionalcontrol valve 25, a pipe 32, the accumulator 24, and a pipe 35. Inheating operation, the four-way directional control valve 25 is switchedover and, as shown by dashed lines in FIG. 2, refrigerant dischargedfrom the compressor 23 is delivered through the pipe 31, the four-waydirectional control valve 25, the pipe 34, and the pipes 41, to theindoor heat exchangers 2 functioning as the condensers. The refrigerantcondensed in the indoor heat exchanger 2 is delivered to the pipes 42,the expansion valve 26 being completely open, the pipe 36, and theoutdoor heat exchanger 22 functioning as the evaporator. The refrigerantvaporized in the outdoor heat exchanger 22 is returned through the pipe33, the four-way directional control valve 25, the pipe 32, theaccumulator 24, and the pipe 35 to the compressor 23.

[0029] In order to evaluate coefficients of performance (COP) of the airconditioner, the inventor variously set internal volumes of the indoorheat exchangers 2 and internal volumes of the outdoor heat exchanger 22with respect to different capacity classes from 2.2 kW to 5.0 kW, asshown in FIGS. 4A and 4B. FIG. 4C shows ratios of the internal volumesof the outdoor heat exchanger 22 to the internal volumes of the indoorheat exchangers 2. Internal volumes of the whole refrigerant circuitvary according to setting of the internal volumes of the indoor heatexchangers 2 and of the internal volumes of the outdoor heat exchanger22.

[0030] In 5.0 kW class, for example, the internal volume of the outdoorheat exchanger 22 was set at 1.45 liters and the internal volume of theindoor heat exchanger 2 was set at 0.47 liter. COP in 5.0 kW class wasmeasured with variation in quantity of refrigerant (total quantity forfilling the refrigerant circuit) and results as shown in FIGS. 1A and 1Bwere obtained. FIG. 1A shows COP in cooling operation and FIG. 1B showsCOP in heating operation. In cooling operation, as is evident from FIG.1A, COP exhibited peak values as high as 2.7 to 2.8 on condition thatthe quantity of R32 refrigerant was 960 g. By contrast, COP of an airconditioner having the same capacity of 5.0 kW with use of R410A was 2.2at maximum (on condition that the quantity of refrigerant was 1300 g).

[0031] Thus a range of quantity of refrigerant providing COP peak onvarious conditions with use of R32 was determined by an experiment. HighCOP was obtained on condition that a filling quantity of singlerefrigerant R32 in the multi-type air conditioner was in a range from120 g to 300 g per kilowatt of refrigerating capacity. High COP wasobtained on condition that the filling quantity of single refrigerantR32 for the refrigerant circuit of the multi-type air conditioner was ina range from 84 g to 300 g per liter of internal volume of thecondenser.

[0032] On condition that the capacities were the same (efficiencies ofthe condensers were equivalent) in a range from 2.2 kW to 5.0 kW,comparison between COP with use of R32 and COP with use of R410Aprovided results as shown in FIGS. 3A and 3B. The quantity ofrefrigerant in the case that R32 was used was optimized in a range from60% to 80% by weight of the quantity of refrigerant in the case thatR410A was used. FIG. 3A shows that COP with use of R32 was 108.1(%)relative to COP (100%) with use of R410A. FIG. 3B shows that COP withuse of R410A was 4.00 whereas COP with use of R32 was 4.33. As isevident from those, COP that is obtained with use of R32 and with thequantity of refrigerant set in an appropriate range may be much higherthan COP with use of R410A. Among factors that thus improve COP areimprovement based on little pressure drop and improvement based onimprovement in heat transfer in the refrigerant and, in addition toimprovement based on physical properties of the refrigerant.

[0033] From FIGS. 1A and 1B, an optimum quantity of refrigerant thatprovides COP peak in use of R32 is found to be 960 g in coolingoperation and to be 840 g in heating operation. On the other hand, anoptimum quantity of refrigerant in use of R410A is found to be 1300 g incooling operation and to be 1100 g in heating operation. With use ofR32, as is evident from these results, a ratio between optimumquantities of refrigerant in cooling operation and in heating operationis closer to 1 than the ratio with use of R410A. Consequently,refrigerant vessels for adjustment between cooling and heating may bemade unnecessary or a capacity of the accumulator may be decreased inthe case of R32.

[0034]FIG. 6 shows differences between optimum quantities of refrigerantin cooling and heating operations, with use of FIGS. 1A and 1B. As shownin FIG. 6, a difference between the optimum quantity of R32 refrigerantin cooling operation and the optimum quantity of R32 refrigerant inheating operation is smaller than that of R410A. R32 achieves a high COPwith a smaller filling quantity of refrigerant in comparison with R410A.That is, R32 has a higher heat transfer capacity in comparison withR410A refrigerant. Thus R32 provides the smaller difference between theoptimum quantity of refrigerant in cooling operation and the optimumquantity of refrigerant in heating operation in comparison with R410Arefrigerant, and achieves a high COP with smaller filling quantity ofrefrigerant in comparison with R410A. Therefore, R32 allows reduction inquantity of refrigerant for use in an air conditioner. FIG. 7 showsvolumes of accumulators and receivers that correspond to refrigeratingcapacities with regard to refrigerants R32, R410A, and R22. As shown inFIG. 7, air conditioners with refrigerating capacities not higher than 4kW do not require accumulators and receivers. That is, air conditionerswith use of R32, which do not require accumulators and receivers, allowreduction in cost of manufacturing the air conditioners andminiaturization of the air conditioners.

[0035] The embodiment has been described as to heat pump airconditioners but is not limited to those. The invention may be appliedgenerally to apparatus that execute refrigerating cycles with use of R32as refrigerant.

[0036] As a matter of course, principles of the invention may be appliednot only to single refrigerant of R32 but also extensively to mixedrefrigerant containing at least 70 percent R32 by weight.

[0037] In an experiment by the inventor where mixed refrigerantcontaining at least 70 percent R32 by weight was used in the multi-typeair conditioner, high COP was obtained on condition that the fillingquantity of R32 in the mixed refrigerant for the refrigerant circuit wasin a range from 370 g to 700 g per kilowatt of refrigerating capacity.When mixed refrigerant containing at least 70 percent R32 by weight wasused in the multi-type air conditioner, high COP was obtained oncondition that the filling quantity of R32 in the mixed refrigerant forthe refrigerant circuit was in a range from 260 g to 700 g per liter ofinternal volume of the condenser.

[0038] As the mixed refrigerant, a mixture of R32 and R125 isconceivable. As for the mixed refrigerant of R32 and R125, as shown inFIG. 5, an R32 content range of up to 70 percent by weight is anazeotropic range in which composition of liquid and composition ofgenerated vapor are the same, and an R32 content range not smaller than70 percent is a nonazeotropic range. Characteristics of R32 appearclearly with increase in content of R32, and the characteristics of R32appear further conspicuously in the nonazeotropic range. That is, R32content not less than 70 percent by weight causes a remarkable increasein energy efficiency and makes it possible to obtain a high COP.

[0039] As shown in FIGS. 1A, 1B, and 5, mixed refrigerant containing atleast 70 percent R32 by weight thus makes COP generally equivalent to orlarger than that provided by conventional refrigerant such as R22.

What is claimed is:
 1. A multi-type refrigerator that executesrefrigerating cycles by circulating R32 as refrigerant through arefrigerant circuit including one outdoor unit having a compressor, acondenser, and expansion means and a plurality of indoor units havingevaporators, the multi-type refrigerator characterized in that a fillingquantity of R32 described above for the refrigerant circuit is in arange from 120 g to 300 g per kilowatt of refrigerating capacity.
 2. Amulti-type refrigerator that executes refrigerating cycles bycirculating R32 as refrigerant through a refrigerant circuit includingone outdoor unit having a compressor, a condenser, and expansion meansand a plurality of indoor units having evaporators, the multi-typerefrigerator characterized in that a filling quantity of R32 describedabove for the refrigerant circuit is in a range from 84 g to 300 g perliter of internal volume of the condenser.
 3. A multi-type refrigeratorthat executes refrigerating cycles by circulating mixed refrigerantcontaining at least 70 percent R32 by weight through a refrigerantcircuit including one outdoor unit having a compressor, a condenser, andexpansion means and a plurality of indoor units having evaporators, themulti-type refrigerator characterized in that a filling quantity of R32described above for the refrigerant circuit is in a range from 370 g to700 g per kilowatt of refrigerating capacity.
 4. A multi-typerefrigerator that executes refrigerating cycles by circulating mixedrefrigerant containing at least 70 percent R32 by weight through arefrigerant circuit including one outdoor unit having a compressor, acondenser, and expansion means and a plurality of indoor units havingevaporators, the multi-type refrigerator characterized in that a fillingquantity of R32 described above for the refrigerant circuit is in arange from 260 g to 700 g per liter of internal volume of the condenser.